In recent years, memory systems comprising a nonvolatile memory are widely used.
As one of such memory systems, a solid state drive (SSD) comprising a NAND flash memory is known. SSD is used as a main storage of various computing devices.
Recently, it is required that a huge amount of data be stored efficiently in a storage.
As technology for improving storage efficiency, de-duplication is known.
But, with the conventional de-duplication technology, the efficiency of garbage collection of the nonvolatile memory is not taken into consideration. The decline in efficiency of the garbage collection may be a factor of degrading the performance of the SSD. In order to realize an SSD which supports de-duplication, the efficiency of garbage collection needs to be fully taken into consideration.